Pavlof Volcano has been erupting for over a week, releasing a humongous plume of ash, steam, and smoke visible from the International Space Station. The eruption has quieted down, but seismic data suggests that it's not over.

ByLiz Fuller-Wright, CorrespondentMay 24, 2013

Space station astronauts captured this picture of Pavlof Volcano on Saturday.

Is it over?

Pavlof has been playing it cool for the past few days, reports the Alaska Volcano Observatory, which celebrated its 25th anniversary last month.

Though the ash eruptions have disrupted local air travel, the violence seems to have subsided for now, with a more relaxed release of ash and lava continuing steadily. Even through the clouds hiding Pavlof from sight, satellites can measure high surface temperatures indicating that the lava is still flowing.

After about a week of steady seismic rumbles, the shaking calmed down on Tuesday morning and hasn't restarted, though a huge seismic blast this morning suggests that Pavlof had another volcanic explosion – but through the clouds, it's hard to know just what or where.

The scientists at Alaska Volcano Observatory have the volcano threat level set at "Watch," which is one step down from the highest level, "Warning." But they caution that massive explosions – like the one that created that giant, 20,000-foot plume – can occur without warning.

The Aleutian Islands are sparsely enough settled that the primary hazard from volcanoes like Pavlof is that airborne ash could endanger planes flying between North America and Asia. In fact, in 1989, a wide-body passenger jet encountered an ash plume from Redoubt, another Alaska volcano, and lost power in all four engines. Fortunately for the passengers, after the plane plummeted two miles in five minutes, the crew restarted the engines and landed safely in Anchorage, about a hundred miles away.

Why did Pavlof erupt?

Like the rest of the Aleutian Islands (and, for that matter, the Cascades), Pavlof sits on the boundary between the Pacific Plate and the North American plate. When the dense ocean floor runs into the less-dense continental crust, its weight pulls it down into the mantle, where the heat and pressures make it start to melt.

When rock melts, magma forms – and when magma reaches the earth's surface, it erupts as lava. The more water or gases were trapped in the magma, the more explosive the eruption will be.

Though scientists know exactly how volcanoes form, volcanologists can't yet predict eruptions. But they've made huge strides, thanks to regular monitoring of hundreds of active volcanoes around the world.

Volcano monitoring became a political punching bag in 2009, after Louisiana's Gov. Bobby Jindal highlighted it as "wasteful spending" in the Republican response to President Obama's State of the Union address. "Instead of monitoring volcanoes, what Congress should be monitoring is the eruption of spending in Washington, D.C.," said Mr. Jindal. The eruption of Redoubt Volcano a month later – the same volcano that had nearly crashed a passenger jet in 1989 – was seen by some as a definitive response, but video monitoring shrunk in recent years due to budget pressures and the sequester.

Alaska's 52 active volcanoes once had 200 working seismic instruments. Now 80 of those instruments have fallen into disrepair and can’t be fixed because of the USGS budget cuts, the Associated Press reported last week. That means that five of Alaska's 52 active volcanoes aren’t monitored electronically at all, and the number could rise if more instruments go without maintenance.